Subscribe to The Chicago Manual of Style Online
Q. Greetings! When using a slash in the abbreviation w/ should there be a space after it or not? E.g., Fluffy went down the street w/Cookie? or Smoochie went to the store w/ Pookie?
A. Add a space. W/ is an abbreviated word, not a prefix. Of course, you would never use w/ in regular, formal writing. It’s more for laundry lists, emails to friends, texts, and so forth.